Physicists believe they have made a huge progress in the concept of time since they have imported its ‘meaning’ into physics from the philosophers in the XVII century.

We understand time dilation in special and general relativity but still we have advanced enough in the notion of time-flow and the meaning of ‘present’.

I will introduce the nowadays hot debate among theoretical physicists according to which time has either disappeared from the equations, like in quantum gravity, or has become ‘fundamental and real’ and we need to re-write the physical laws.

In this last case: what if the the laws of physics were not timeless? What if they could evolve?

The continuation of an incoherent discussion of emission by atoms and molecules in astrophysical plasmas. A quick recap of forbidden lines will be followed by a discussion diatomic molecules and recombination processes.

IceCube has recently reported the discovery of high-energy neutrinos of astrophysical origin, opening up the PeV (10^15 eV) sky. These observations are challenging to interpret on the astronomical side and have triggered a fruitful collaboration across particle and astro-physics. I will first discuss neutrinos in an astronomical context. I will then make the case for extreme blazars, i.e. strong, very high energy gamma-ray sources of the high energy peaked type, to be the counterparts of at least some of the IceCube neutrinos. This scenario is supported by positional and energetic matches, theoretical modelling, and Monte Carlo simulations and has been confirmed very recently by the detection of gamma-ray emission from an extreme blazar within the error circle of an IceCube event. The talk is self-contained, requires no previous knowledge of neutrinos or blazars, and has been prepared for a very broad audience.

Information field theory (IFT) provides probabilistic image reconstruction algorithms for incomplete and noisy data. Numerical information field theory (NIFTy) is a Python library for IFT algorithms. We provide a short introduction into the usage of NIFTy for astronomical data with a practice oriented demo, covering the Wiener filter and radio interferometric imaging. NIFTy is maintained by the IFT group at the MPI for Astrophysics and is available here: https://gitlab.mpcdf.mpg.de/ift/NIFTy

Gravitational lensing allows us to weigh distant objects, measure cosmological distances, and get a super-resolved view of very distant sources. Its various regimes (strong lensing, weak lensing, microlensing and variations on these themes) have manifold applications in contemporary astrophysics.

In this mini-lecture, I will start with an overview of the basic principles and formalism, and some quick numbers for different astrophysical regimes. The second part of this mini-lecture will present a birdseye view of applications, somewhat biased towards topics that I have worked upon.

I will keep the formalism to a minimum. Links to more exhaustive materials will be provided with the slides.

Interstellar clouds, filling the space between stars, may be revealed thanks to either some spectral features originating in very rarefied gas or to the selective attenuation of the starlight, known as interstellar extinction. Selectivity means that a star, shining through a cloud or clouds is more red than intrinsically as the extinction is higher in blue range than in red. This is why extinction is nicknamed "reddening".

Extinction is being carried by dust particles of the submicron size. They are believed to be originated in vicinities of mass-loosing stars and then - to evolve in the interstellar space from bare to core-mantle ones.

However, grains, seen in any individual cloud, may be apparently seriously of different size, shape and chemical/cristalline composition. In a vast majority of cases one observes distant stars through several clouds, seeing thus an ill-defined average(s) which are very difficult to be interpreted in terms of any physical theory.

Currently I try, together with Ralf Siebenmorgen and Jonathan Smoker, to retrieve and compare extinction laws in several individual interstellar clouds.

The hydrogen Lyman-alpha line is extremely important in many fields of astrophysics. In particular, this UV line is conveniently redshifted to the visible and near infrared wavelength ranges for high-redshift objects, making it observable from the ground. The hydrogen Lyman-alpha thus provides the main observational window on the formation and evolution of high redshift galaxies. However, this resonant line undergoes complex radiation transfer effects, which need careful modelling in order to extract information on the kinematics and geometry of the gas. This information is thus enclosed in the line shape. In this lesson I will briefly introduce the emission mechanisms for this line and explain the resonant scattering process.

The baryon cycle refers to the complex physical processes by which gas travels into, through, and out of galaxies. In this lecture, I will first review simulation and observational results which, together, have provided important fresh clues on the physics of galactic gas flows. I will then discuss prospects of detecting the circumgalactic medium in emission and other future progress which will likely impact galaxy formation studies at all cosmic epochs.